There is longstanding debate in the field of rangeland management about the perceived benefits of a rotational or adaptive grazing system utilizing higher stock density and shorter grazing periods in a pasture or paddock. The belief that rotational or adaptive grazing can reduce animal selectivity, increase carrying capacity, improve plant productivity, and increase species composition has led ranchers to adopt this strategy. Unfortunately, the scientific research has not found a positive correlation between rotational grazing and the benefits ranchers claim to incur (Briske et al. 2008; Teague et al. 2008). The functional mechanism driving differences between grazing systems are the management induced diets of cattle. Understanding how these diets are driven is paramount to resolving this debate and assisting ranchers in reaching production and conservation goals. The goal of this research is to provide ranchers with an accurate assessment of the differences in cattle nutrition, which is a function of what cattle eat, in an adaptive rotational grazing management strategy compared to a traditional continuous season-long grazing strategy. Ultimately, this will quantify the production and conservation trade-offs associated with each system in northern-mixed grass prairie and shortgrass steppe ecosystems. The funding will allow us to use the novel DNA metabarcoding analysis of fecal samples to discern, with a high level of accuracy, the diet composition of cattle to the plant genus or species level. This information will be coupled with Near Infrared Spectroscopy (NIRS) for nutritional performance (Lyons and Stuth 1992), and high resolution pedometers for animal activity for which we already have financial support. By collecting this data using new and detailed technology, the impact of grazing strategy on animal nutrition and behavior will give ranchers a better decision-making tool when deciding what grazing strategy will help them meet their operation objectives. Our project will move beyond anecdotes and provide quantitative data of the latest technological insight into what cattle eats, why they eat it relative to grazing managmenet, and how it influences animal performance. Research will be presented at Wyoming Extension events, the American Society of Animal Science annual meeting, stakeholder meetings, and the Society for Range Management annual meeting.
The overall goal of this research is to provide ranchers with a decision-making tool to implement a grazing system that will fit their individual operation goals.
1. To determine how grazing management strategy influences diet composition of yearling cattle at USDA ARS grazing experiments near Cheyenne, Wyoming and Nunn, Colorado. Specifically, does the diet of animals in an adaptive grazing management strategy contain more or different plant species than continuous season-long grazing strategy? Are animals consuming plants that are not considered to typically be eaten by cattle?
2. Quantify how cattle diet composition correlates with nutritional plane and performance data derived from NIRS (such as crude protein and digestibility)? In other words, how do the specific plants that are in the diet correlate to crude protein and digestibility levels, and ultimately, daily gains.
3. Determine how the diet of yearling cattle eat relates to energy expenditures and activity levels in cattle in different grazing systems. Are animals in adaptive grazing management systems spending more time walking and looking for palatable plant species?
To test the validity of DNA Metabarcoding analysis, we ran a feeding trial in February-March of 2017. Five individually penned animals (open cows/heifers), were weighed and fed a diet of grass hay prior to beginning the experiment. Cattle were fed at maintenance in mixed diets and ad libitum on homogenous diets across the entire experiment. We designed six diets using 1) cool season grass hay (Alopecurus arundinaceus), 2) alfalfa (Medicago sativa), 3) warm season hay (Setaria italic), 4) a mix of warm season hay, cool season hay and alfalfa, 5) equal mix warm season hay, cool season hay, alfalfa and a minor component of sagebrush (Artemisia tridentata), 6) Alfalfa + minor components of blue grama (Bouteloua gracilis), western wheatgrass (Pacopyrum smithii), and crested wheatgrass (Agropyron cristatum). All diets were fed for one week and fecal samples from individual animals were taken on day seven. All samples were immediately frozen after sampling and sent to the Jonah Ventures lab for analysis.
Ranchers interested in this project across Wyoming and part of Nebraska were asked to fecal sample their herds during peak growing season (June, July, and August). Sampling kits were sent to ranches or extension agents with interested ranches in their area. Fecal samples were collected by sub-sampling ten individual fecal pats and combining them into a herd composite. After samples were taken, they were put on ice and sent back to the High Plains Grasslands Research Station, processed, and sent to the Jonah Ventures lab for analysis. Data has come back from the lab and we will be creating tailored reports to each individual ranch (some wish to remain anonymous). All ranches were asked to send in pasture information so that we can understand the results more easily and have a good idea of what occurs on their operation.
Preliminary results indicate that this technology is fairly good at picking up major components, but does not allow for minor components to be accurately detected in the diet. Explicit analysis results and discussion forthcoming.
We will be analyzing this data based on individual operations and will need to ask permission by ranch prior to sharing results from their operations.
Educational & Outreach Activities
Some ranchers have expressed interest in a webinar or workshop discussing how the methodology works so we are hoping to do this in the future.
Thus far, most of our outreach has been via email or during small workshops put on by other organizations. We are hoping to conduct a workshop/presentation of how this technology works in the near future. I have discussed the methodology at 2 range workshops. We will be sending individual operations their results as soon as we have finished with the analysis and will be asking ranches if we can use their data to write a paper about what cattle in Wyoming are eating regionally during the summer grazing season.
By understanding what cattle are eating and what time they are eating it, ranchers may be able to adjust their grazing management system to either protect vulnerable species or target graze invasive species on their landscape. This allows them to tailor their grazing systems in a more sustainable way to restore the integrity of their land.
My knowledge of extension and outreach (and the importance of good relationships with ranch managers) greatly increased over the course of this project. This project has made me want to be more involved in applied research in regional settings and allowed me to develop skills in coordinating larger scale research. My advisor has spent a large portion of his academic career in extension and outreach and I believe the relationships he developed with his constituents allowed this project to be successful. The eager involvement of the ranching community in this project has opened my eyes to the possibilities of more collaborative research in the future. Once our analysis is done, we will all have a much greater understanding of what cattle are selecting for during the summer grazing season.